Detection and quantification of maternal-effect gene transcripts in mouse second polar bodies: potential markers of embryo developmental competence.

OBJECTIVE: To test the hypothesis that quantification of messenger RNAs originating from the second polar body (PB(2)) provides a noninvasive tool for assessing embryo quality. DESIGN: Prospective study. SETTING: Hospital-based academic research laboratory. ANIMAL(S): CD1 female mice. INTERVENTION(S): Metaphase II oocytes obtained from 7- to 8-week-old mice after pregnant mare's serum gonadotropin and hCG priming. After in vitro fertilization, the PB(2) was biopsied from zygote, followed by reverse transcription. Real-time polymerase chain reaction was performed to quantify gene expression levels in single PB(2). The sibling zygotes were continuously cultured to blastocyst stage. MAIN OUTCOME MEASURE(S): Embryo developmental competence and six maternal-effect gene (Dnmt1, Mater, Nobox, Npm2, Tcl1, and Zar1) transcripts in the PB(2). RESULT(S): Second polar body messenger RNA was detected in all candidate genes. Transcripts that were present in greater abundance in the zygote were more likely to be detected in quantitative polymerase chain reaction replicates from single PB(2). Four candidate genes (Dnmt1, Nobox, Npm2, and Tcl1) expression levels in PB(2) between two groups (two-cell embryo vs. blastocyts) approached statistical significance. CONCLUSION(S): Second polar bodies may contain a representative transcript profile to that of the zygote after fertilization. Differences in gene expression in PB(2) may be potential biomarkers of embryo quality.